operator

lib/model.js

@@ -640,6 +640,23 @@ logicalOperators.$not = function (obj, query) {
 };
 
 
+/**
+ * Use a function to match
+ * @param {Model} obj
+ * @param {Query} query
+ */
+logicalOperators.$where = function (obj, func) {
+  var result;
+
+  if (!_.isFunction(func)) { throw "$where operator used without a function"; }
+
+  result = func.call(obj);
+  if (!_.isBoolean(result)) { throw "$where function must return boolean"; }
+
+  return result;
+};
+
+
 /**
  * Tell if a given document matches a query
  * @param {Object} obj Document to check

test/model.test.js

@@ -1172,6 +1172,24 @@ describe('Model', function () {
     });
 
 
+    describe('Logical operator $where', function () {
+
+      it('Function should match and not match correctly', function () {
+        model.match({ a: 4}, { $where: function () { return this.a === 4; } }).should.equal(true);
+        model.match({ a: 4}, { $where: function () { return this.a === 5; } }).should.equal(false);
+      });
+
+      it('Should throw an error if the $where function is not, in fact, a function', function () {
+        (function () { model.match({ a: 4 }, { $where: 'not a function' }); }).should.throw();
+      });
+
+      it('Should throw an error if the $where function returns a non-boolean', function () {
+        (function () { model.match({ a: 4 }, { $where: function () { return 'not a boolean'; } }); }).should.throw();
+      });
+
+    });
+
+
     describe('Array fields', function () {
 
       it('Field equality', function () {